BackgroundTo ensure an efficient and targeted adaptation with low injury risk during strength exercises, knowledge of the participant specific internal loading conditions is essential. The goal of this study was to calculate the lower limb muscles forces during the strength exercises deadlifts, goodmornings and splits squats by means of musculoskeletal simulation.

Methods11 participants were assessed performing 10 different variations of split squats by varying the step length as well as the maximal frontal tibia angle, and 13 participants were measured performing deadlift and goodmorning exercises. Using individualised musculoskeletal models, forces of the Quadriceps four parts, Hamstrings four parts and m. gluteus maximus three parts were computed.

ResultsDeadlifts resulted highest loading for the Quadriceps, especially for the vasti 18–34 N-kg, but not for the rectus femoris 8–10 N-kg, which exhibited its greatest loading during split squats 13–27 N-kg in the rear limb. Hamstrings were loaded isometrically during goodmornings but dynamically during deadlifts. For the m. gluteus maximus, the highest loading was observed during split squats in the front limb up to 25 N-kg, while deadlifts produced increasingly, large loading over large ranges of motion in hip and knee.

ConclusionsActing muscle forces vary between exercises, execution form and joint angle. For all examined muscles, deadlifts produced considerable loading over large ranges of motion, while split squats seem to be highly dependent upon exercise variation. This study provides key information to design strength-training programs with respect to loading conditions and ranges of motion of lower extremity muscles.